Security is an important concern in the realm of documents and digital production and/or reproduction of same. Known digital image printing/copying systems produce documents of such high quality that a need has been identified to prevent effective printing/copying of certain documents such as high-value printed items including tickets, financial instruments, security passes, and the like. Known techniques include printing the original document in a manner such that it includes a digital “watermark” using only conventional paper and toner or ink. A digital watermark in a broad sense can be defined as information, for example one or more letters, words, symbols or patterns, that is at least partially (preferably fully or at least substantially) hidden in a printed image under normal viewing conditions but that is more clearly discernable under certain specialized viewing conditions. Unauthorized reproduction of documents including such digital watermarks typically degrades or obscures the digital watermark, which can aid in detection of counterfeit documents.
FIG. 1 is a simplified enlarged illustration of a conventional halftone gloss mark GM structure that is one type of known digital watermark that can be defined and created using only standard materials, i.e., conventional ink/toner colorants (e.g., cyan, magenta, yellow and black) and conventional media such as printing or “copy” paper. The gloss mark GM includes a gloss mark object GO such as one or more characters, symbols, patterns or the like (shown in FIG. 1 as an italicized “A”) defined in a printed document D against a background GB of the same color, wherein the gloss mark object GO and background GB are defined using respective first and second anisotropic halftone dot structures. When the document D is viewed straight-on (i.e., with the line of sight being at least generally orthogonal to the paper or other media on which the document D is printed) or when the document D is scanned for copying on a conventional image reproduction apparatus, the first and second halftone structures of the gloss mark object GO and background GB are perceived or sensed to be a substantially uniform color halftone area. If the printed document D is viewed at an oblique angle, however, there will be a significant difference in the light reflected from the respective first and second halftone structures of the gloss mark object GO and background GB, which will allow the gloss mark object GO to be readily perceived by a human viewer. As such, any attempt to produce a counterfeit of the original document via scanning and reproduction will degrade or obliterate the gloss mark because the image reproduction apparatus will not accurately distinguish between the different halftone structures GO,GB.
For real world applications, these known halftone gloss marks GM can be printed with any one of a wide variety of different colors but require that the gloss mark object GO have a certain minimum size of about 24 points or larger (where 1 point= 1/72 of an inch), based upon the spatial requirements of the first and second anisotropic halftone dot structures. Also, a halftone gloss mark object defined at a certain point size cannot simply be scaled to a new font size. Instead, the gloss mark object must be defined for each different size. Furthermore, these halftone gloss marks must also be sized in integer multiples of pixels/lines. As such, it has been deemed desirable to provide a method and apparatus for producing a high resolution and scalable gloss effect that overcomes these and other limitations of halftone gloss marks.